Voltage-gated Ca2+ channels and Ca2+ regulate the electrical and biochemical properties of hair cells (HCs) and spiral ganglia neurons (SGNs). However, the cellular mechanisms of the Ca2+-mediated functions remain unclear. The overall goal of this proposal is to deploy innovative molecular biological, electrophysiological, and imaging techniques, many inspired from previous Ca2+ channel studies, for the discovery of fundamental and newly accessible arenas of Ca2+ channel and Ca2+-mediated physiology in HCs and SGNs. This proposal drives three aims that address various aspects of HC and SGN Ca2+ channel physiology, each with fundamental and therapeutic implications. The overall hypothesis is that multiple Ca2+ channels in HCs and SGNs regulate distinct functions, ranging from short-term membrane excitability to long-term developmental processes and gene expression. For example, we predict that the Cav1.2 channel is expressed in SGNs, serving both as a channel and as a transcription factor. The Aims are: (1) To unequivocally resolve the distinct properties and functions of the subtypes of Ca2+ channels in HCs and SGNs. The identity and functions of the Ca2+ channels other than the Cav1.3 subtype remain uncertain, despite large potential physiological ramifications. We have identified 7 distinct spliced variants of Cav3.1 and predict that alternative splicing of mRNA produces distinct functional Cav3.1, which are specific to HCs. Additionally, we have strong evidence to suggest that SGNs deploy several other non-Cav1.3 channels to promote distinct functions. (2) To continue to define the role of Ca2+ entry through distinct channels in regulating local and global Ca2+ domains in HCs and SGNs. (3) To identify the distinct Ca2+ channel subtype/s that serve as transcriptional factors in SGNs. We predict SGNs express conventional and unconventional neuronal Ca2+ channels, including the 11C-cardiac Ca2+ channel (Cav1.2). We hypothesize that under normal conditions, the Cav1.2 channels serve mainly as a transcriptional factor in SGNs, bridging the gap between the plasma membrane and the nucleus. The role of Ca2+-mediated activation of other physiologically important transcriptional factors such as CREB will be delineated. The project will be conducted using mice, and physiological and biochemical tools. Overall, this proposal will answer fundamental unknowns of Ca2+-mediated electrical and biochemical changes in HC and SGN physiology. Hair cells (HCs) in the inner ear convert sound and balance signals into electrical impulses, which are then transmitted to spiral ganglia neurons (SGNs) with remarkable precision and sensitivity. Our long-term goal is to understand how Ca2+ channel proteins and Ca2+ ions regulate the electrical activity and biochemistry of HCs and SGNs. Studies from our group and others have demonstrated that Ca2+-mediated changes underlie electrical activity of HCs and SGNs and indeed, Ca2+ may turn on genes that are responsible for neuronal survival. We know very little about the different Ca2+ channels that confer Ca2+-dependent changes in HCs and SGNs, despite their potential therapeutic ramifications. Strong evidence from data in developmental cell biology and electrophysiology motivates our overall hypothesis that multiple Ca2+ channels in HCs and SGNs regulate distinct functions ranging from short-term membrane excitability to long-term developmental processes and gene expression. For example, we predict that the channel Cav1.2 is expressed in SGNs, serving as a channel as well as a transcription factor. These studies should reveal how HCs and SGNs coordinate and regulate their electrical and biochemical machinery, information that might be exploited to induce HC and SGN survival after damage.